Crosshair - 10 dbic Circularly polarized antenna tutorial!

[Joe90]

Super !

thanks to both for taking the time to answer

[Joe90]

What happen if I use a really small reflector ?

My idea is to point the antenna directly to the zenith and be able to fly all around and over me.
a 3db ''hemisphere'' would be really nice because no null over me and a decent range.

[HugeOne]

The back of the elements are of opposite polarization, all is fine when they receive the reflection from the panel.
When the the panel get too small, you loose your circularity a lot on the sides. Also front to back ratio will become a problem.
7.5db is the lowest I could get.

-Hugo

[Joe90]

I understand, Thanks,

I will give it a try anyway the beam width is pretty wide like this.
Even pointed to the sky the theorical range would still be like 2km horizontal (side of the beam)
It's not that I want to fly high but it is nice to be able to go everywhere when thermalling.
This is what I am looking to do this summer.

After trying this one I may build a second and use diversity this will do even better.

Regards

[HugeOne]

It's not that I want to fly high but it is nice to be able to go everywhere when thermalling.

Staked fan?

[Joe90]

I know this model but it is the null in top that is annoying.

I tried the 7db crosshair and I can fly almost over me without problems :-)
The only thing left is the emmiting antenna null on the glider pointing at me while circling.
But this is just when high and close which dont happen too much.
Someone has worked a diversity system that eliminate this problem. (If I remember, sircana made this with 2 x 2.4ghz antennas)

This antenna work like a charm.

Another question: How much I have to strive to maintant le coax in the center of the balun ?
It was touching the balun and the picture was ok. I put a silicon tubing over it and the picture improve (better colors)
Still not in perfect center
Can I center it with a small conductor spacer at the weld point an the bottom ?
a weld wire made like this: --o--
the center part holding the coax and extremities soldered on the balun ends ?

[HugeOne]

I use a solder spacer at the bottom to keep coax centered and a small piece of silicone tube at the top. The balun is essentially a coax filled with air (don't fill it with a tube or whatever) with a shorted end.
A coax, to work optimally, need to have the conductor centered.

-Hugo

[Haych]

Hi all. I made one of these crosshairs for 1280 MHz last week and tested with a CL on a fox800 VTx. Made it to 6 km (my furthest to date) with perfect signal . It was made with the minimum size reflector too so I should be able to easily fit it to my new tracker. ... this one's a keeper.

Thanks to IBC and HugeOne.

[SPG]

Just thought I would share my Crosshair made to 2510Mhz.
I used some 150mm square PCB for the reflector.
22.8mm of 10mm Diam brass tube for the balun.
Some 0.63mm coper wire for the elements.
An RG223 cable with a SMA connector on it.
Food container for the protector (not glued down yet).
I didn't use any element supports as they will be protected. I also put 1mm of insulation under the elements so they can't make contact with the balun.

I'm very happy with the results. AS you can see from the VSWR test I'm getting a bit over 1.2! The band width is pretty wide too.
I wasn't sure the 10mm tube and thicker coax would workout with Ibcrazys dimensions, but they were pretty much spot on.
I made the hole I made in the reflector just big enough to fit the cable. I then soldered all around the cable jacket to the reflector it to help keep things centred which may of helped with the balun.
They are much easier to build than the helical. Going to make another one now and a 1.3G for a friend.

Cheers,
SPG.

[IBCrazy]

^ That antenna looks nothing short of excellent. Fly it and enjoy it. Don't bother with supports if you have a cover

-Alex